Some kinds of skates, mainly with in-line rollers, are already known in the art to be provided with a chassis including two carriages that are movable relative to each other. So, for instance, the French patent application No. 96 01439 discloses a skate with four in-line rollers mounted in a two-by-two arrangement to a front carriage and a rear carriage, respectively. The two carriages are pivotally hinged on to a chassis, on which the footwear thereabove is intended to rest. The two carriages cross each other in the central zone of the skate, such that the rear roller of the front carriage comes to lie behind the front roller of the rear carriage. This solution, although proving particularly advantageous in enabling small obstacles as may be found on the skating surface to be surmounted, involves a considerable instability of the skate during regular skating, wherein such instability of the skate turns out as being particularly marked during the initial and final pushing phases of a skating stride, i.e. when the skate starts being pushed and then stops being pushed. In the initial pushing phase, the skater exerts a progressive force from the heel portion towards the toe portion, whereas in the terminal pushing phase, such force is solely exerted on the toe portion by tipping, i.e. inclining the skate forwards so as to enable the leg to perform a complete stride. In the skate as described in the French patent application No. 96 01439 it therefore occurs that, during the initial pushing phase, the force exerted onto the heel portion is transferred—via the pivoting connection of the rear carriage to the chassis—to the second and the fourth roller belonging to the rear carriage; thereupon, the force is transferred from the heel portion to the toe portion and, thus, from the second and the fourth roller to the first and third roller belonging to the front carriage. Therefore, the rear carriage progressively changes from a situation in which it is subjected to maximum load (i.e. initial thrust), to a situation in which it on the contrary is fully unloaded, possibly even raised from the ground (end of thrust), and vice-versa as far as the behaviour of the front carriage is concerned. This practically means that, at any moment throughout skating, one of the two carriages is not being loaded adequately, with the possibility for it to freely pivot about the hinging pin connecting it to the chassis in the initial and final thrust phases. This obviously involves the skater being substantially unable to adequately control the carriage not being loaded, and this is exactly what determines the afore-mentioned instability of the skate, particularly when skating at a high speed.
The solution depicted in the U.S. Pat. No. 6,227,550 is only partially effective in solving the above-mentioned instability problem, since the rear and front carriages, connected in an articulated manner to the chassis and supporting a respective pair of alternately arranged rollers, wherein the first and third rollers are supported by the front carriage and the second and fourth rollers are supported by the rear carriage, have arms connected to the chassis via a vibration damping member interposed therebetween. In this manner, the oscillation of the carriages under no-load conditions, i.e. when no force is applied from the foot of the skater, is controlled and kept within limits by said vibration damping members. However, owing to the arms of the carriages being so connected to the chassis, the way in which such embodiment operates is more similar to the one of conventional rigid chassis, in which the rollers are supported by the vertical walls of the chassis. In fact, during the initial pushing phase, it is the rear roller that is in contact with the running or sliding surface, whereas this is true for the front roller during the final thrust phase.
The U.S. Pat. No. 5,904,359 discloses a skate, in which both the sole of the footwear, i.e. boot, and the chassis are comprised of two parts that are movable relative to each other; to the rear part of the sole there is in fact rigidly connected the rear part of the chassis, and the same applies to the respective front parts. The two parts of the sole are joined in an articulated manner to each other, whereas the two parts of the chassis are connected to each other slidably. In this way, the structure of the boot follows the natural bending motion of the foot, thereby keeping at least two rollers in contact with the running or sliding surface throughout the skating stride, i.e. from the beginning to the end thereof. However, in the initial pushing phase and the end-of-thrust phase it is the two rear rollers and the two front rollers, respectively, that are in contact with the running surface. This most obviously involves a clear difficulty in riding, directing and controlling the skate in said phases: in fact, the sole rear rollers being in contact in the initial pushing phase is instrumental in determining a condition of instability of the toe portion exactly when the maximum force is being applied, whereas the sole front rollers being on the contrary in contact during the final phase causes again a condition of instability to arise in the toe portion due to no rest, i.e. backing, being available at the rear when the force applied by the foot is eventually fully removed.